public class Solution3 {
    public String addBinary(String a, String b) {
        int cur1 = a.length() - 1;
        int cur2 = b.length() - 1;
        int t = 0;
        StringBuffer ret = new StringBuffer();
        while(cur1 >= 0 || cur2 >= 0 || t != 0) {
            if(cur1 >= 0) {
                t += a.charAt(cur1) - '0';
                cur1--;
            }
            if(cur2 >= 0) {
                t += b.charAt(cur2) - '0';
                cur2--;
            }
            ret.append((char)('0' + (char)(t % 2)));
            t /= 2;
        }
        ret.reverse();
        return ret.toString();
    }
}
